Copper-lead mattes are intermediate products obtained in copper and lead metallurgy. The chemical composition of such copper-lead mattes varies widely in dependence on the primary raw materials employed, e.g. within the ranges (by weight) of 15 to 50% copper, 10 to 60% lead, 0 to 30% iron, 10 to 25% sulfur. Varying amounts of arsenic, antimony, tin and nickel may also be contained in such mattes.
In the processing which is usual in the prior art, low-copper copper-lead mattes having a copper content below 35% are concentrated to copper contents of about 45% by melting them together with copper-containing materials, such as high-copper slags.
This process is usually carried out in a shaft furnace and, in addition to a more highly concentrated copper-lead matte, produces crude lead, which is subsequently refined.
The more highly concentrated copper-lead matte contains about 12 to 18% by weight lead and is subjected to a blowing treatment in Pierce-Smith converters to form converter copper. In that process mainly lead and iron are oxidized by means of atmospheric oxygen and are then taken up by a converter slag formed by an addition of silica-containing materials. Only part of the lead (about 20%) and part of other liquid materials are incorporated in the fine dust discharged from the converter.
This process has several disadvantages, including high consumption of fossil energy carriers, such as coke for the shaft furnace process, expensive preparation of the burden for the shaft furnace, formation of exhaust gases which have a low SO.sub.2 content and thus cannot be used to produce sulfuric acid, distribution of the impurities of the copper-lead matte, such as lead and arsenic, to the various intermediate products formed in the shaft furnace and the converter, intermittent operation of the converter, and pollution of the environment by the emission of dust and gas adjacent to the shaft furnace and the converter.
In copper metallurgy, various other processes are known by which crude copper can be produced continuously from primary raw materials. In these processes the starting materials are copper sulfide ores or concentrates which contain impurities, such as lead, arsenic, antimony, in amounts which are very low relative to the copper content.
In all continuous processes, it is desired to achieve advantages as regards economy, energy consumption and processing technology, as well as substantial ecological improvements (Engineering and Mining Journal, 173 (8), pages 66 to 68; Journal of Metals, 16 (5), pages 416 to 420; Journal of Metals, 24 (4), pages 25 to 32).
Published German Application DE-OS No. 29 41 225 discloses a continuous process for the pyrometallurgical production of copper from sulfide ores or concentrates. In that process the ores are melted to produce matte and primary slag and the matte is converted to blister copper and converter slag.
To reduce the losses of copper in slags, particularly in primary slags, the melting process is carried out with a high surplus of oxygen and a matte having a relatively high copper content is obtained, the copper contained in the primary slag and in the converter slag being recovered by a reduction process.
The process is not intended for use in the processing of low-copper ores and cannot be used to process copper-lead matte having a high lead content.
In the process known from German Patent Publication DE-AS No. 19 22 599 for the production of copper from materials which contain copper sulfide, the molten bath, which contains nickel in considerable amounts, is maintained in a state of high turbulence at temperatures above 1300.degree. C. and after part of the impurities have been volatilized is blown with an oxidizing agent and the copper sulfide is converted to liquid copper and is refined further.
In the examples of that prior publication, nickel contents up to about 14% are mentioned as well as contents up to 0.2% of each of the impurities Se, As, Bi, Pb.
In this latter process it is essential to adjust and maintain a predetermined ratio of copper to nickel so that arsenic can be effectively eliminated and the noble metals can be effectively concentrated in the metal phase, which is immiscible with the liquid matte phase. A continuous processing is not disclosed and copper-lead matte is not used.